req.answer.vote is not a function"

My code is alright, and all my dependencies installed. however when I call the vote-up POST i get the error above. The code in my route.js file is as follows:

'use strict' const express = require('express'); const router = express.Router(); const Question = require('./models'); router.param("qID", (req, res, next, id) => { Question.findById(id, (err, doc) => { if (err) next(err); if (!doc) { err = new Error("Not found"); err.status = 404; return next(err); } req.question = doc; return next(); }); });

router.param("aID", (req, res, next, id) => { req.answer = req.question.answers.id(id);

if (!req.answer) {
    err = new Error("Not found");
    err.status = 404;
    return next(err);
}

return next();

}); //GET /questions //route for getting questions router.get('/', (req, res) => { // Return all the questions Question.find({}) .sort({ createdAt: -1 }) .exec((err, questions) => { if (err) return next(err); res.json(questions);

    });

}); //POST /questions //route for creating questions router.post('/', (req, res) => { let question = new Question(req.body); question.save((err, question) => { if (err) return next(err); res.status(201); res.json(question); }); // Return all the questions

}); //GET /questions/:id //route for getting questions router.get('/:qID', (req, res) => { // Return all the questions res.json(req.question);

}); //POST /questions/:id/answers //route for creating questions router.post('/:qID/answers', (req, res) => { // Return all the req.question.answers.push(req.body); req.question.save((err, question) => { if (err) return next(err); res.status(201); res.json(question); }); });

//PUT /questions/:qid/answers/:id //Edit a specific answer router.put('/:qID/answers/:aID', (req, res) => { // Return all the questions req.answer.update(req.body, (err, result) => { if (err) return next(err); res.json(result); });

});

//DELETe /questions/:qid/answers/:id //Delete a specific answer router.delete('/:qID/answers/:aID', (req, res) => { // Return all the questions req.answer.remove((err) => { req.question.save((err, question) => { if (err) return next(err); res.json(question); });

});

});

// POST/questions/:qID/answers/:aID/vote-up // POST/questions/:qID/answers/:aID/vodte-down // Vote on a specific answer router.post("/:qID/answers/:aID/vote-:dir", function(req, res, next) { if (req.params.dir.search(/^(up|down)$/) === -1) { var err = new Error("Not Found"); err.status = 404; next(err); } else { req.vote = req.params.dir; next(); } }, function(req, res, next) { req.answer.vote(req.vote, function(err, question) { if (err) return next(err); res.json(question); }); });

module.exports = router;

And my models.js file is as follows

'use strict' const mongoose = require('mongoose'); const Schema = mongoose.Schema; let sortAnswers = function(a, b) { // -negativ a before b // 0 no change //+ postive a after b if (b.votes == a.votes) { return b.updatedAt - a.updatedAt; } return b.votes - a.votes; } const AnswerSchema = new Schema({ text: String, createdAt: { type: Date, default: Date.now }, updatedAt: { type: Date, default: Date.now }, votes: { type: Number, default: 0 } }); const QuestionSchema = new Schema({ text: String, createdAt: { type: Date, default: Date.now }, answers: [AnswerSchema] }); AnswerSchema.method("update", function(updates, callback) { Object.assign(this, updates, { updatedAt: new Date() }); this.parent().save(callback) });

AnswerSchema.method("vote", function(vote, callback) { if (vote === "up") { this.votes += 1; } else { this.votes -= 1; } this.parent().save(callback); });

QuestionSchema.pre("save", function(next) { this.answers.sort(sortAnswers); next(); });

module.exports = mongoose.model('Question', QuestionSchema)